Convert tic-tac-toe demo program to use the stamps concept

[mvines]

Before a user can play tic-tac-toe they need platform tokens to drive the game. At the moment this means an airdrop, in the future it means obtaining tokens from another user, an exchange, or ___? Avoiding this barrier for programs that are willing to fund the user for the purposes of interacting with them is highly desirable.

#1754 is an attempt to solve this problem.

Let's try to implement this approach or something like it for tic-tac-toe. Evidence of success would be that the user no longer needs an airdrop to play the game.
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[mvines]

Done, see solana-labs/example-tictactoe@d9faee6

The player funding works as follows:

1. The player passes their public key to the dashboard server
2. Dashboard server constructs a transaction that atomically (a) assigns the player's account to the tic-tac-toe program, and (b) transfers 1 token to the player's account. Dashboard server signs the transaction with its secret key and returns the transaction to the player
3. The player also signs the transaction with their secret key and submits it. Once confirmed the player now has 1 token that can only be used by them to initiate a new tic-tac-toe game or join the existing game advertised on the dashboard.
4. Every time the player spends their 1 token to advance their game, the dashboard transfers 1 additional token to the player's account for their next move.

Confession: I cheated slightly, in that the client actually has access to the dashboard account's secret key for player funding. See https://github.com/solana-labs/example-tictactoe/blob/d9faee6118489f50e28c71703e85b09682c3e680/src/program/tic-tac-toe-dashboard.js#L144-L167. This shortcut was taken simply to avoid building out a bunch more client/server plumbing that would make the demo even more complex but does not change the underlying player funding mechanism in any way.